1. Field of the Invention
The present invention generally relates to a vehicle mounted bearing assembly such as a wheel support bearing assembly for supporting a wheel of an automotive vehicle and, more particularly, to the vehicle mounted bearing assembly of a type that is equipped with a rotation detecting sensor used as a component part of an automobile anti-lock control system.
2. Description of the Prior Art
In an automobile anti-lock braking system or the like, the necessity has long been recognized to detect the number of revolutions or rotational speed of one or more vehicle wheels so that the behavior of the vehicle wheels tending to skid can be controlled. A rotation detecting sensor employed in an automotive vehicle for this purpose is generally incorporated in a wheel support bearing assembly that is used to support a vehicle wheel. A detected rotation signal outputted from the rotation detecting sensor that is indicative of the rotational speed of the wheel is generally supplied from the wheel support bearing assembly to an external control box installed at a remote location outside the wheel support bearing assembly but within a vehicle body structure by means of a signal transmitting cable.
As is well known to those skilled in the art, electric wiring including not only the signal transmitting cable but also electric power supply lines and extending from the rotation detecting sensor within the wheel support bearing assembly to the external control box is generally routed via and, hence, exposed to the outside space between the rotation detecting sensor and the external control box. Accordingly, it has often been observed that some of the electric lines forming the electric wiring, including those of the signal transmitting cable are damaged or broken upon collision with gravel stones or rocks or under the influence of freeze-up of a tire house. In order to alleviate those problems, the assignee of the present invention has suggested in the Japanese Laid-open Patent Publication No. 2001-151090 a wireless transmission system by which a detected rotation signal outputted from a rotation detecting sensor can be transmitted wireless to an external control box provided within a vehicle structure.
According to the above mentioned publication, it has been found involving a problem in that since the detected rotation signal outputted form the rotation detecting sensor is in the form of an analog signal, the detected rotation signal is susceptible to external noises. The existing anti-lock braking system now in use appears to pose no problem and works satisfactorily even though the detected rotation signal in the form of an analog signal is transmitted wireless.
However, the site where the wheel support bearing assembly is installed is under a severe condition susceptible to change in temperature and full of muddy water and/or dusts and, moreover, the automotive vehicle has a number of sources of external noises that adversely affect the wireless transmission of signals. Thus, considering that the rotation detecting sensor is placed under such a severe condition and in a manner susceptible to influences brought about by the external noises, it appears that the existing anti-slid braking system lacks a sufficient reliability particularly where a highly trustworthy anti-lock control is desired.
While the conventional sensor-equipped wheel support bearing assembly is designed to use the rotation detecting sensor for the sole purpose of detecting the rotational speed of the wheel, the inventors of the present invention have now devised to make the best use of the detected rotation signal from the rotation detecting sensor and a transmission unit for transmitting the rotation signal wireless for a different purpose of monitoring the vehicle mounted bearing assembly such as a wheel support bearing assembly so that the presence or absence of an abnormality in functionality of the vehicle mounted bearing assembly can be diagnosed.